This invention relates to an adjustable support leg and, more particularly, to legs used in connection with tripods and similar devices. It is understood that tripods are generally employed to support cameras, optical instruments, antenna, and the like.
Numerous suggested constructions for support legs for tripods and the like have been suggested over the years. The major desired attributes of such devices are stability and ease of adjustment. One suggested device has been provided by Grimal in U.S. Pat. No. 2,940,708. Grimal proposes tripod legs made of channeled or transversely arcuate members, with each leg comprising two telescoping members. The lower member of each leg is intended to be movable with respect to the upper member so as to adjust the relative height of the tripod. A clamping means is provided at the lower end of the upper member. This clamping means is used to engage and releasably join the two members together to thereby form each tripod leg.
Still another suggested device is set forth by Wittel in U.S. Pat. No. 2,019,753. Wittel suggests tripod legs having two telescoping members. The lower member engages, within the upper member, an expansible nut. The lower member portion is adjusted by relieving the nut, moving the lower member with respect to the upper member, and expanding the nut by rotating the lower member threaded therein.
Still another device of this nature is suggested by Dalton in U.S. Pat. No. 2,668,682. The device suggested by Dalton comprises tripos legs in which the upper member of each leg is an inverted A-frame with the lower member inserted through a bore recess at the apex of the A. The assembly is secured by a narrowing or tightening of the diameter of the bore by means of a hand knob. Additional support is provided by a spider secured to the center of the tripod seat and at the apex of each A-frame leg.
Still another device of this type, intended to overcome the problems of support and stability, is revealed by Mercier, Son in U.S. Pat. No. 765,980. This device has an upper member of a tripod which has a substantially rectangular shape and has a transverse slot. A lower rectangular member is secured to the rear of the upper member by means of a threaded screw, a wing nut, and a washer. The wing nut is tightened against the washer which pulls the two members against one another.
The prior art devices have a number of obvious disadvantages. First, in most of the devices it is apparent that the entire weight of the supported object is directed against the means for joining the upper and lower members. If a heavy object such as a motion picture or television camera was supported on the tripod over a long period of time, the constant weight upon the means for joining might cause the joined members to move with respect to one another. Thus, for example, the device by Dalton focuses the weight of the object supported by the tripod at the bore or apex of the A-frame. The devices of Wittel, Grimal, and Mercier, Son similarly provide that the weight of the object be borne at the point of joining the two members.
It should also be noted that the devices of the type suggested by Wittel, Dalton, and Grimal must be adjusted at the base or footing which is certainly inconvenient. Furthermore, the Wittel device must be adjusted by lifting the entire tripod and rotating the lower member with respect to the upper member.
An additional inconvenience is provided by the device suggested by Mercier, Son. Loosening the wing nut would cause the two members to pivot at the screw, further disorienting the entire tripod.